In general, in an electrostatic recording apparatus, an electrostatic latent image is written on an electrostatic latent image carrier such as a photoreceptor or a dielectric body; the electrostatic latent image is electrostatically developed with developer so that an electrically charged toner image is formed; the electrically charged toner image is electrostatically transferred onto a recording medium such as a sheet of recording paper; and the toner image is fixed onto the recording medium by heat, pressure or light.
A single drum type multicolor recording apparatus is well known as a multicolor recording apparatus in which the above electrostatic recording technique is used. In this single drum type multicolor recording apparatus, a single electrostatic latent image carrier, for example, a photoreceptor drum is used, and a plurality of developing units are arranged between an electrostatic latent image writing position at which the image is written on the photoreceptor drum and a transfer unit. In this case, developer having a toner component for one color is used for each developing unit. For example, in the case of full color recording, there are provided 4 developing units. In these developing units, developers having toner components of yellow, cyan, magenta and black are respectively used. On the photoreceptor drum, for example, an electrostatic latent image is recorded according to image data of yellow, and the thus recorded electrostatic latent image is developed by yellow toner. Then the yellow toner image is transferred onto a recording sheet and fixed. Next, on the photoreceptor drum, for example, an electrostatic latent image is recorded according to image data of cyan, and the thus recorded electrostatic latent image is developed by cyan toner. Then the cyan toner image is transferred onto a recording sheet on which the yellow toner image has been formed, and then the transferred cyan toner image is fixed. The same image forming process is conducted on the image data of magenta and black. In this way, toner images of 4 colors are superimposed on the recording sheet, and image recording of full color is accomplished. The above single drum type multicolor recording apparatus is advantageous in that the overall arrangement can be made relatively compact, however, it is necessary to form a toner image of each color with the single photoreceptor drum. Accordingly, it is impossible to form a multicolor image at high speed.
As another type multicolor recording apparatus in which the electrostatic recording technique is used, there is provided a multi-drum type multicolor recording apparatus. In the case of full color recording conducted by this multi-drum type multicolor recording apparatus, 4 sets of electrostatic recording units are used, in which each unit is assembled into the aforementioned electrostatic recording apparatus. These electrostatic recording units are arranged in series along a recording sheet conveyance path. When a recording sheet passes through the electrostatic recording units, toner images of respective colors are transferred and superimposed on the recording sheet. Due to the foregoing, a full color image is formed on the recording sheet.
As described above, the multi-drum type multicolor electrostatic recording apparatus is advantageous in that multicolor recording can be accomplished at high speed. However, since a plurality of electrostatic recording units are arranged in series in the multi-drum type multicolor electrostatic recording apparatus, the dimensions of the structure are increased, which causes a problem in the practical use of the recording apparatus.
In order to accomplish recording a multicolor image of high quality by the multi-drum type multicolor electrostatic recording apparatus, it is necessary that an electrostatic latent image is stably developed at high speed by the electrostatic latent image developing apparatus used in each electrostatic recording unit.